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Point Machines on London Underground

From the early days of electric traction and automatic signalling on the London Underground, point machines were developed for pneumatic operation.  They have remained the principal type across the system ever since.  The main reason for their survival is that the air supply is already used for trainstops and is therefore available and the speed of operation is twice that for electric points.  The following three photos show a standard LU points mechanism for a set of points near Camden Town (Northern Line).

Fig. 1:   Standard LU Four Foot Point Machine

This is the standard LU "four foot" air operated points mechanism looking from the air cylinder end.  The wooden plank normally covering the mechanism is removed here to show the equipment.  There is a wooden ramp at each end which is provided to reduce the risk of damage from or to equipment which might be hanging from trains. Photo by Tube Troll.

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Fig. 2:   Four Foot Point Machine at the Ground Lock End

This is the standard LU "four foot" air operated points mechanism looking from the ground lock end.  The wooden plank normally covering the mechanism is removed.  Photo by Tube Troll.

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Fig. 3:   Four Foot Point Machine with Detector Box Open

Points mechanism showing the mechanical and electrical locking systems used to secure points in the correct position and verify the locking. Photo by Tube Troll.

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